In numerous applications, apart from a rotational-speed or speed measurement of a periodic scale or an indicator object, also recognition of the direction of movement and/or change of the direction of movement, such as the rotational direction of a wheel or a shaft, often is used. To this end, magnetoresistive sensors for determining the rotational speed and the rotational direction generally are used.
Magnetoresistive sensors are based on the magnetoresistive effect and may, for example, comprise a layer sequence, the electrical resistance of which between two contacts, depends on a relative angle between an impressed magnetic field and an external sensor magnetic field, with the impressed magnetic field being fixed for a given magnetoresistive (MR) sensor. With the aid of the change in resistance, the relative location of the impressed magnetic field with respect to the external sensor magnetic field, and particularly the relative location between the indicator object (for the sensor magnetic field) and the field-sensor means may thus be determined. Magnetoresistive sensors are often based on the GMR (giant magnetic resistance) effect, and the corresponding sensors are referred to as GMR sensors.
In magnetoresistive sensors in, e.g., a speed, angle, direction-measuring device, the necessary signal processing is performed by a digital signal processor means (DSP), for example. The digital signal processor means takes over functions, such as compensation of adjustment deviations, reduction of the hysteresis, and the like. In the automobile branch, for example, it is necessary to monitor rotational directions of machines with high accuracy and reliability. This may be done by processing the signals in a digital context (i.e., in a low-frequency range). However, there are also areas for which analog processing (so-called pre-processing) of signals or at least real-time or at least prompt change-of-direction recognition would be desirable.